1. Field of the Invention
The present invention relates generally to pumping balloons and, more particularly, to temporary cardiac support systems.
2. Related Art
There are a number of medical conditions in which it is necessary or desirable to aid blood flow in a patient. For example, during the performance of surgical procedures such as certain types of open heart surgery, external means are required to completely assume the blood pumping function of the heart to maintain adequate circulation to body organs such as the brain and the heart itself. In other situations, body organs require blood flow which the body is incapable of sufficiently providing due to a failing, traumatized or infarcted heart.
It has been recognized that in these and other situations, it is preferable to have blood pumped in a pulsatile manner, similar to the pumping action of the normal heart. A common approach has been to provide cardiac assistance by introducing a balloon into the circulatory system, commonly the thoracic aorta, and causing the balloon to cyclically inflate and deflate in some relationship with the rhythm of the patient's heart. Such cardiac assist systems of this type are commonly used to assist the left ventricle of the heart, which bears the primary responsibility for systemic circulation, and is most frequently in need of assistance. The most common configuration of the pumping cycle is the "counterpulsation" mode, in which the pumping balloon is inflated during the diastolic portion of the natural cycle to increase blood pressure, and deflated during the systolic portion of the natural cycle to decrease blood pressure and resistance to the left ventricle's natural pumping action. This reduces the load on the left ventricle and raises aortic pressure to increase the blood flow to the coronary and carotid arteries.
Such cardiac assist systems are commonly used due to the limited trauma associated with their implementation. The pumping balloon is generally implemented as a collapsible structure that can be introduced into any large artery, such as a femoral, as part of a standard catheterization procedure. Once introduced into the circulatory system, the pumping balloon is guided into a desired location of the circulatory system. As such, implementation of cardiac assist pumping balloons generally do not require major thoracic or otherwise invasive surgery. Exemplary conventional cardiac assist systems of this type are disclosed in U.S. Pat. Nos. 4,080,958, 4,692,148, 4,077,394, 4,154,227, 4,522,195, 4,407,271 and 4,697,574, the disclosures of which are hereby incorporated by reference herein in their entirety.
U.S. Pat. Nos. 5,820,542 and 5,827,171 disclose various complex designs for intravascular circulatory assist devices involving a pumping membrane such as an inflatable balloon, disposed within an expandable housing structure such as another balloon. The pumping membrane thus divides the outer housing into an intermediate control chamber and an interior pumping chamber. Injection and evacuation of a control/fluid into the control chamber deflates (pumps) and inflates (refills) the pumping chamber. Expandable and collapsible stents are disclosed as one mechanism to expand and retain the control chamber in its maximum dimension while control fluid is withdrawn.
U.S. Pat. Nos. 4,902,272 and 4,785,795 represent important advances in the art of cardiac support systems. Unlike the above cardiac assist systems that adjust systemic pressure to assist a natural heart, these latter patents disclose apparatuses and techniques for directly pumping blood. U.S. Pat. No. 4,902,272 discloses a catheter-based intra-arterial cardiac support system that includes one or two valves that are mounted upstream and downstream of a cyclically inflatable pumping balloon synchronized with the cardiac cycle. One disclosed embodiment provides assistance to the left ventricle through the placement of the pumping balloon in the descending aorta with a balloon valve located distally relative to the natural heart. The balloons are individually inflated and deflated to directly pump blood. The pumping action is peristaltic in nature and operated in phased relationship to the systole and diastole of the natural heart.
U.S. Pat. No. 4,785,795 discloses a catheter-based, high-frequency intra-arterial cardiac support system that includes an externally controlled pumping balloon and balloon valve. The pumping balloon and valve are positioned in a major artery downstream of a natural heart, and are operated at a pumping frequency that is at least three times the normal frequency of the heart to directly pump blood. To assist a left ventricle, for example, the balloon pump is located in the ascending aorta between the aortic valve and the ostium innominate artery. The pumping balloon and valve are sequentially operated to pump blood from the left ventricle into the arterial tree. To assist the right ventricle, the pumping balloon is located in the pulmonary track immediately downstream from the pulmonary valve. The pumping balloon and valve are sequentially operated to pump blood from the right ventricle into the pulmonary trunk. In each application, the balloon valve is positioned downstream of the pumping balloon; that is, the pumping balloon is positioned between the balloon valve and the natural aortic or pulmonary valve.
Although these approaches overcome the above-noted drawbacks associated with traditional cardiac assist systems by directly pumping blood to support or replace the pumping action of the heart, they too have limits to their effectiveness. Unlike conventional pumping balloons, these latter two approaches operate with the pumping balloon interposed between two valves in an otherwise closed region of the circulatory system. The valves may be natural or balloon valves, depending on the embodiment of the cardiac support system. The inventor has observed that at times during certain operations of such devices, the surrounding valves simultaneously occlude the vessel at least momentarily while the pumping balloon deflates. Such an occurrence creates temporarily a vacuum within the vessel region. At times this vacuum is sufficient to draw the vessel walls inward with the deflating pumping balloon. This reduces the effective pumping displacement of the pumping balloon, thereby reducing the overall effectiveness of these cardiac support systems.